1. Field of the Invention
The present invention relates to an internal combustion engine with a valve train having rocker arms which are spherically supported at proximal end portions thereof and abut with engine valves at operating portions thereof and camshafts disposed above the rocker arms.
2. Description of the Related Art
Conventionally, JP-A-2000-161025 discloses an internal combustion engine with a valve train of this kind. In this internal combustion engine, the valve train comprises rocker arms which abut with valve stems at one end and which are spherically supported at the other end thereof by pivot ends fitted in mount holes in a cylinder head and camshafts disposed above the rocker arms. Cams rotating together with the camshaft are brought into sliding contact with rollers which are rotatably supported at central portions of the rocker arms and oscillate the rocker arms about the other end thereof which acts as an oscillating fulcrum, so as to operate valves to open and close.
Incidentally, in the related art, in assembling the rocker arms and the camshaft to the cylinder head, firstly, the rocker arms are assembled to the cylinder head such that one ends thereof are abutted with the valves slidably held in the cylinder head and the other ends thereof are supported on the pivot ends fitted in the mount holes in the cylinder head. Then the camshaft is lowered toward the rocker arms which are already assembled to the cylinder head, from above the rocker arms so assembled and is then assembled to the cylinder head in such a manner that the cams come into contact with the rollers of the rocker arms. However, since they are spherically supported at the other end thereof, the rocker arms tend to tilt in the axial direction of the camshaft. Then, when attempting to assemble the camshaft to the cylinder head in a state where the rocker arms tilt at an angle larger than an angle through which the rocker arms so tilting can be corrected through the contact with the cams assembled to the cylinder head or in a state where the rocker arms are fallen, there may occur a risk that the rocker arms come off or the surfaces of the cams which are formed of a material having a lower hardness than that of the abutment portions of the rocker arms with the cams are damaged through the contact with the abutment portions.
Due to this, when assembling camshafts, it is necessary to secure a state where the rocker arms occupy preset positions or positions at which the rocker arms do not tilt as resulting when the cams are in abutment with the rocker arms or a state where while the rocker arms slightly tilt, the tilt can be corrected through the abutment with the cams so that the rocker arms can occupy the preset positions. Therefore, a tremendously long time has been needed for assembling the camshafts.
To cope with this problem, it has been desired to provide in an internal combustion engine with a valve train having such rocker arms fall-preventive unit for preventing the fall of the rocker arms when the camshafts are assembled to thereby improve the assembling properties of the camshafts and to make the fall-preventive unit flexible in application depending upon layouts of the rocker arms relative to peripheral components.
In addition, conventionally, a camshaft holder is disclosed in JP-A-6-299807 as this type of integral cam holder for an internal combustion engine. In this camshaft holder (corresponding to the cam holder), crossbars for connecting both longitudinal side walls of the camshaft holder are integrally formed at positions corresponding to journal portions of an intake camshaft and an exhaust camshaft, respectively. An intake-side cam journal portion and an exhaust-side cam journal portion are formed on an upper surface of each of the crossbars. Thus, the camshaft holder is given a ladder frame construction, thereby increasing the rigidity thereof. Then, cam journal portions are formed on a lower surface of a cam cap which rides on an upper surface of the camshaft holder at positions corresponding, respectively, to the intake-side and exhaust-side cam journal portions of the crossbar. The cam caps are then bolted to a cylinder head together with the camshaft holder, whereby the camshafts are pivotally supported therebetween.
In general, it is preferable to increase the rigidity of the cam holder in order to secure stable valve train operations over the full operating range of the internal combustion engine. In this respect, according to the related art, since the cam cap to which the intake-side cam journal portion and the exhaust-side cam journal portion are connected is fastened to the crossbar, it is considered that the rigidity of the camshaft holder is increased further by the cam caps so constructed. However, in a case where a cam cap on which only an intake-side cam journal portion is formed and a cam cap on which only an exhaust-side cam journal portion is formed are used as a cam cap such that the separate cam caps are fastened to the crossbar, it is difficult to increase further the rigidity of the camshaft holder by the cam caps so constructed.
The invention was made in view of these situations, and a first object of the invention is to prevent the fall of rocker arms which are supported on spherical surfaces in an axial direction of camshafts so as to facilitate the assembly of the camshafts from above the rocker arms to thereby improve the assembling properties of an internal combustion engine with a valve train. Further, a second object of the invention is to provide an integral cam holder in which bearing portions provided adjacent to each other in an axial direction of a camshaft and primary and secondary longitudinal frames for connecting the bearing portions to each other are formed integrally, the rigidity of the integral cam holder being increased without depending upon the form of camshaft supporting members which are connected to the cam holder for rotatably supporting the camshaft.
According to a first aspect of the invention, there is provided an internal combustion engine with a valve train, comprising:
a rocker arm having a proximal portion which is spherically supported by an oscillating support member and an operating portion abutting with an engine valve;
a camshaft having a cam adapted to be brought into sliding contact with the rocker arm and disposed above the rocker arm, wherein the engine valve is operated to open and close by the rocker arm which is oscillated by the cam which rotates together with the camshaft; and
fall-preventive units provided in such a manner as to face both sides of the rocker arm in an axial direction of the camshaft, for preventing the fall of the rocker arm in the axial direction through the contact with the rocker arm.
According to the construction, even in case the rocker arm which is supported on the spherical surface tries to fall in either of the axial directions, the rocker arm comes into contact with either of the fall-preventive units which are provided to face the sides of the rocker arm, whereby the fall of the rocker arm can be prevented. Consequently, according to the first aspect of the invention, the following advantage can be provided. Namely, even if the rocker arm which is supported on the spherical surface tries to fall in either of the axial directions, since the fall-preventive units are provided to face the sides of the rocker arm, the rocker arm comes into contact with either of the fall-preventive units, whereby the fall of the rocker arm can be prevented. Therefore, since there is no risk that the rocker arm falls or comes off when the camshaft is assembled, the assembly of the camshaft which is disposed above the rocker arm can be facilitated, and moreover, there is no risk that cam surface of the cam is damaged by the rocker arm. As a result, a time required for assembling the camshaft can be reduced to thereby improve the assembling properties of the internal combustion engine with such a valve train.
Further, according to a second aspect of the invention, there is provided an internal combustion engine with a valve train, comprising:
a rocker arm having a proximal portion which is spherically supported by an oscillating support member and an operating portion abutting with an engine valve;
a camshaft having a cam adapted to be brought into sliding contact with the rocker arm and disposed above the rocker arm, wherein the engine valve is operated to open and close by the rocker arm which is oscillated by the cam which rotates together with the camshaft; and
a fall-preventive unit provided on a member which face the cam and the rocker arm in an axial direction of the camshaft for preventing the fall of the rocker arm in the axial direction through the contact with the rocker arm, the fall-preventive unit projecting further in the axial direction toward the rocker arm than a surface of the member which faces the cam.
According to the construction, even in a case where the rocker arm is spaced away from the member which faces the cam and the rocker arm, the projection can be made to project close to the rocker arm by making use of the member. Then, in the event that the rocker arm which is supported on the spherical surface attempts to fall, the rocker arm come into contact with the projection, whereby the fall thereof can be prevented. Consequently, according to this construction, the following advantage can be provided. Namely, since the fall-preventive unit is provided on the member which faces the cam and the rocker arm in the axial direction, and moreover, since the fall-preventive unit projects further toward the rocker arm than the surface of the member which faces the cam, even in case the rocker arm is spaced relatively far away from the member in the axial direction, the fall of the rocker arm can be prevented with the simple construction in which the projection is made to project closer to the rocker arm by making use of the member which faces the cam and the rocker arm. Then, in case the rocker arm which is supported on the spherical surface attempts to fall in the axial direction, the rocker arm comes into contact with the projection situated close thereto, whereby the fall of the rocker arm can be prevented. Therefore, since there is no risk that the rocker arm falls or comes off at the time of assembling the camshaft, the assembly of the camshaft that is disposed above the rocker arm can be facilitated, and moreover, there is no risk that the cam surface of the cam is damaged by the rocker arm. As a result, a time required for assembling the camshaft can be reduced to thereby improve the assembling properties of the internal combustion engine with such a valve train.
Moreover, according to a third aspect of the invention, there is provided an internal combustion engine with a valve train, comprising:
a rocker arm having a proximal portion which is spherically supported by an oscillating support member and an operating portion abutting with an engine valve;
a camshaft having a cam adapted to be brought into sliding contact with the rocker arm and disposed above the rocker arm, wherein the engine valve is operated to open and close by the rocker arm which is oscillated by the cam which rotates together with the camshaft; and
a fall-preventive unit provided in such a manner as to face only one side of the rocker arms in an axial direction of the camshaft for preventing the fall of the rocker arm in the axial direction through the contact with the rocker arm,
wherein the center of gravity of the rocker arm is situated at a position where a moment is generated that tilts the rocker arm toward the one side.
According to the construction, in a state where the rocker arm which is supported on the spherical surface is slidably supported, in case the rocker arm tries to fall due to the generation of a moment attributed to the position of the center of gravity thereof, the rocker arm comes into contact with the fall-preventive unit which is only provided on the side to which the rocker arm try to fall, whereby the fall thereof can be prevented. Consequently, according to the invention, the following advantage can be provided. Namely, since the fall-preventive unit is provided in such a manner as to face only one side of the rocker arm in the axial direction and the center of gravity of the rocker arm is situated at a position where a moment is generated that tilts the rocker arm to the one side thereof in a state where the rocker arm which is in abutment with the engine valve is supported by the oscillating support member, even in a case where there is no space on the one side of the rocker arm in the axial direction for providing the fall-preventive unit, in the event that the rocker arm which is supported on the spherical surface tries to fall due to the generation of moment attributed to the position of the center of gravity thereof with the rocker arm being pivotally supported, the rocker arm comes into contact with the fall-preventive unit provided on the side thereof to which the rocker arm tries to fall, whereby the fall thereof can be prevented. Thus, since the weight of the internal combustion engine can be reduced when compared with one in which the fall-preventive units are provided on the sides of the rocker arms and there is no risk that the rocker arm falls or comes off when the camshaft is assembled, the assembly of the camshaft that is disposed above the rocker arm can be facilitated, and moreover, there is no risk that the cam surface of the cam is damaged by the rocker arm. As a result, a time required for assembling the camshaft can be reduced to thereby improve the assembling properties of the internal combustion engine with such a valve train.
An internal combustion engine with a valve train as set forth in any of the first to third aspect of the invention, wherein the fall-preventive unit faces an upper end portion of the rocker arm which faces the cam in a vertical direction.
According to the construction, since the fall-preventive unit comes into contact with the upper end portions or area in the vicinity thereof of the falling rocker arm which includes a location which is farthest away from the falling center and which faces the cam in a vertical direction, the degree of tilt of the rocker arms when it comes into contact with the fall-preventive unit can be reduced. Consequently, according to the fourth aspect of the invention, in addition to the advantages provided by the cited aspects of the invention, the following advantage can be provided. Namely, since the fall-preventive unit faces the upper end portion of the rocker arm which faces the cam in the vertical direction and this allows the fall-preventive unit to come into contact with the upper end portion or the area in the vicinity thereof of the rocker arm which includes the location which is farthest away from the falling center, the degree of tilt of the rocker arms when it comes into contact with the fall-preventive unit can be reduced. Thus, the assembly of the camshaft can further be facilitated, and the assembling properties of the internal combustion engine with such a valve train can be improved.
An internal combustion engine with a valve train as set forth in any of the first to fourth aspects of the invention, wherein the member on which the fall-preventive unit is provided is a bearing portion for rotatably supporting the camshaft, and wherein the fall-preventive unit is a projection which is integrally formed on a side of the bearing portion which faces the rocker arm in the axial direction.
According to the construction, since the projection is integrally formed on the bearing portion whose rigidity is reduced due to the formation of a bearing bore, the rigidity of the bearing portion can be increased. Consequently, according to the fifth aspect of the invention, in addition to the advantages provided by the cited aspects of the invention, the following advantage can be provided. Namely, since the fall-preventive unit is the projection which is integrally formed on the side of the bearing portion for rotatably supporting the camshaft which faces the rocker arm in the axial direction, the rigidity of the bearing portion can be increased by making use of the projection for preventing the fall of the rocker arm.
According a sixth aspect of the invention, there is provided an integral cam holder for an internal combustion engine which is fastened to a cylinder head, comprising:
a plurality of bearing portions being provided at intervals in an axial direction of a camshaft of a valve train for operating engine valves to open and close, for rotatably supporting the camshaft;
primary and secondary longitudinal frames situated at end portions of each of the bearing portions and extending in the axial direction while connecting the bearing portions which are adjacent to each other in the axial direction at first connecting portions, the primary and secondary longitudinal frames being integrally formed with each other, wherein a rocker arm of the valve train is disposed in a through space which is formed by being surrounded by the adjacent bearing portions and the primary and secondary longitudinal frames, and
a partitioning portion connected to the primary and secondary longitudinal frames at second connecting portions between the adjacent bearing portions in such a manner as to be integrally formed with the primary and secondary longitudinal frames, for partitioning the through space in the axial direction to thereby form small through spaces.
According to the construction, the primary and secondary longitudinal frames are connected to each other by the partitioning portion between the respective pairs of adjacent bearing portions, and moreover, the partitioning portion is provided in such a manner as to partition the through space in which the rocker arm is provided to thereby form the small through spaces. Consequently, the first aspect of the invention provides the following advantages. Namely, since the primary and secondary longitudinal frames which are connected to the adjacent bearing portions of the cam holder are connected by the partitioning portion between the adjacent bearing portions, the rigidity of the cam holder can be increased without depending upon the form of the camshaft supporting member which is connected to the cam holder for rotatably supporting the camshaft. In addition, since the partitioning portion partitions the through space which is formed by being surrounded by the adjacent bearing portions and the primary and secondary longitudinal frames and in which the rocker arm is disposed in the axial direction to thereby form the small through spaces, an increase in weight of the cam holder can be suppressed which would otherwise take place due to the provision of the partitioning portion.
According to a seventh aspect of the invention, there is provided an integral cam holder for an internal combustion chamber as set forth in the sixth aspect of the invention, wherein a plurality of the rocker arms are disposed in the through space at intervals in the axial direction, and wherein the partitioning portion is disposed between the rocker arms which are adjacent to each other in the axial direction in such a manner as to overlap the rocker arms as viewed in the axial direction.
According to the construction, in forming the partitioning portion, a space can be utilized which is formed between the rocker arms of the plurality of rocker arms disposed between the adjacent bearing portions which are adjacent to each other in the axial direction. Consequently, according to the seventh aspect of the invention, the following advantage is provided in addition to the advantage provided by the sixth aspect of the invention. Namely, since the space can be utilized for the formation of the partitioning portion which is formed between the plurality of rocker arms disposed in the through space at intervals in the axial direction which are adjacent to each other in the axial direction by constructing the partitioning portion so as to be disposed between the plurality of rocker arms so disposed which are adjacent to each other in the axial direction in such a manner as to overlap the rocker arms as viewed in the axial direction, the enlargement of the cam holder in the axial direction thereof can be avoided which would otherwise take place due to the provision of the partitioning portion.
According an eighth aspect of the invention, there is provided an integral cam holder for an internal combustion chamber as set forth in the sixth aspect of the invention, wherein a fastening portion for fastening the cam holder to the cylinder head is formed at the second connecting portion between the primary longitudinal frame and the partitioning portion.
According to the construction, the number of fastening portions on the cam holder to the cylinder head can be increased. Consequently, according to the eighth aspect of the invention, in addition to the advantages provided by the cited aspects of the invention, the following advantage is provided. Namely, since the number of fastening portions on the cam holder to the cylinder head can be increased by forming the fastening portion for fastening the cam holder to the cylinder head at the second connecting portion between the primary longitudinal frame and the partitioning portion, the rigidity of the cam holder can be increased further.
According to a ninth aspect of the invention, there is provided an integral cam holder for an internal combustion engine as set forth in the sixth or seventh aspect of the invention, wherein a primary oil passage is formed in the primary longitudinal frame,
wherein a fastening portion for fastening the cam holder to the cylinder head is formed at the first connecting portion between the primary longitudinal frame and the bearing portion or the second connecting portion between the primary longitudinal frame and the partitioning portion,
wherein the fastening portion forms an oil feed passage adapted to communicate with the primary oil passage and to feed lubricating oil to a hydraulic lash adjuster which is mounted on the cylinder head in such a manner as to come into abutment with the rocker arm, and
wherein the oil feed passage connects to a secondary oil passage formed in the cylinder head so as to communicate with the lash adjuster.
According to the construction, the sealing pressure at the connecting portion between the oil feed passage and the secondary oil passage is increased at the fastening portion where the oil feed passage and the secondary oil passage is connected by virtue of the fastening by a fastening member. Consequently, according to the ninth aspect of the invention, on top of the advantages provided by the cited aspects of the invention, the following advantage is provided. Namely, by the construction wherein the primary oil passage is formed in the primary longitudinal frame, wherein the oil feed passage for feeding lubricating oil to the lash adjuster is formed in the fastening portion formed at the first connecting portion between the primary longitudinal frame and the bearing portion or the second connecting portion between the primary longitudinal frame and the partitioning portion for fastening the cam holder to the cylinder head, and wherein the oil feed passage connects to the secondary oil passage at the fastening portion the sealing pressure at the connecting portion between the oil feed passage and the secondary oil passage is increased at the fastening portion where the oil feed passage and the secondary oil passage is connected by virtue of the fastening by the fastening member, and therefore, the sealing property of the oil feed passage for the lash adjuster at the connecting portion can be improved by making use of the fastening portion for fastening the cam holder to the cylinder head, this contributing to the improvement in the response in operation of the lash adjuster.
Note that when used in the specification the xe2x80x9caxial directionxe2x80x9d means the direction of the rotational axis of the camshaft.